Velocity profiles in mitral blood flow based on three-dimensional freehand colour flow imaging acquired at high frame rate

To describe the mitral blood flow velocity distribution, we applied a freehand dynamic three-dimensional (3D) colour flow method using a moving sample surface that followed the mitral apparatus during diastole. Nineteen healthy volunteers were studied. The ultrasound data were captured from 10-20 heartbeats at high frame rate (mean 46 frames/s) while freely tilting the transducer in an apical position. A magnetic position sensor system recorded the spatial position and orientation of the probe. Blood flow velocities were integrated across a spherical surface. In volumetric blood flow measurements this would yield angle independence of the Doppler beam. Raw digital data were analysed off-line with no loss of temporal resolution. The ratio of the maximum velocity time integral (VTI) to the mean VTI was mean 1.3 (range 1.1-1.6). At the time of peak flow the ratio of the maximum to the mean velocity was mean 1.5 (range 1.2-2.6). The blood flow velocity profile was non-uniform. By using a single sample volume in Doppler measurements of the maximum VTI errors ranging from 10 to 60% may be introduced in calculations of stroke volumes.